U.S. patent number 4,762,408 [Application Number 06/880,515] was granted by the patent office on 1988-08-09 for progressive multifocal lens and spectacles using same.
This patent grant is currently assigned to Seiko Epson Corporation. Invention is credited to Toshihide Shinohara.
United States Patent |
4,762,408 |
Shinohara |
August 9, 1988 |
Progressive multifocal lens and spectacles using same
Abstract
Progressive multifocal ophthalmic lenses are provided having a
far vision viewing zone, a near vision viewing zone and an
intermediate vision viewing zone therebetween. A central basic
curve extends essentially vertically through the far, intermediate
and near vision viewing zones. The sizes of the zones and
configuration of the zones are set by predetermined conditions and
equations. The construction provides improved lenses for use
especially where intermediate and near vision viewing is
required.
Inventors: |
Shinohara; Toshihide (Suwa,
JP) |
Assignee: |
Seiko Epson Corporation (Tokyo,
JP)
|
Family
ID: |
15498480 |
Appl.
No.: |
06/880,515 |
Filed: |
June 30, 1986 |
Foreign Application Priority Data
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|
|
|
|
Jul 9, 1985 [JP] |
|
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60-150512 |
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Current U.S.
Class: |
351/159.42 |
Current CPC
Class: |
G02C
7/061 (20130101); G02C 7/065 (20130101); G02C
7/066 (20130101) |
Current International
Class: |
G02C
7/02 (20060101); G02C 007/06 () |
Field of
Search: |
;351/168,169,159 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
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4537479 |
August 1985 |
Shinohara et al. |
|
Primary Examiner: Corbin; John K.
Assistant Examiner: Kachmarik; Ronald M.
Attorney, Agent or Firm: Kaplan; Blum
Claims
What is claimed is:
1. A progressive multifocal ophthalmic lens comprising first and
second refractive surfaces, said first refractive surface having a
central basic curve defined thereon which extends essentially
vertically therealong and divides said first refractive surface
into a left portion and a right portion, and including a far vision
viewing zone in an upper portion for viewing mainly distant
objects, a near vision viewing zone in a lower portion for viewing
mainly nearby objects, and an intermediate vision viewing zone for
viewing mainly intermediate objects between said far and near
vision viewing zones, said far vision viewing zone and said near
vision viewing zone each having an optical center and a clear
vision viewing zone, a predetermined additional power being added
between the optical center of the far vision viewing zone and the
optical center of the near vision viewing zone along said central
basic curve, the gradient G of the focal power variation between
said optical center of the far vision viewing zone and said optical
center of the near vision viewing zone satisfying the
condition:
wherein ADD is said additional power in units of diopter,
the far vision viewing zone in the portion above said optical
center of said far vision viewing zone having said clear vision
viewing zone including said central basic curve and defined by the
condition:
where n is the refractive index of the lens material, and C1 and C2
are the principal curvatures at each point on the refractive
surface of the lens, and wherein m.sup.-1 =1/meter,
the maximum width W (mm) of the said clear vision viewing zone in
said far vision viewing zone satisfying the condition:
2. The progressive multifocal lens as claimed in claim 1, wherein
said gradient G of the focal power variation satisfies the
condition:
3. The progressive multifocal lens as claimed in claim 1 wherein
said principal curvatures C1 and C2 along said central basic curve
in said far vision viewing zone satisfies the condition:
and the direction of the maximum curvature of said principal
curvatures is nearly parallel to the horizontal direction.
4. The progressive multifocal lens as claimed in claim 2 wherein
said principal curvatures C1 and C2 along said central basic curve
in said far vision viewing zone satisfies the condition:
and the direction of the maximum curvature of said principal
curvatures is nearly parallel to the horizontal direction.
5. The progressive multifocal lens as claimed in claim 1 wherein
said intermediate vision viewing zone includes a clear vision
viewing zone, and wherein the maximum width of the clear vision
viewing zone in said far vision viewing zone and the maximum width
of the clear vision viewing zone in said near vision viewing zone
does not exceed by four times the minimum width of the clear vision
viewing zone in the intermediate vision viewing zone.
6. The progressive multifocal lens as claimed in claim 2 wherein
said intermediate vision viewing zone includes a clear vision
viewing zone, and wherein the maximum width of the clear vision
viewing zone in said far vision viewing zone and the maximum width
of the clear vision viewing zone in said near vision viewing zone
does not exceed by four times the minimum width of the clear vision
viewing zone in the intermediate vision viewing zone.
7. Spectacles having at least one progressive multifocal lens set
in a frame thereof, said progressive multifocal ophthalmic lens
comprising first and second refractive surfaces, said first
refractive surface having a central basic curve defined thereon
which extends essentially vertically therealong and divides said
first refractive surface into a left portion and a right portion,
and including a far vision viewing zone in an upper portion for
viewing mainly distant objects, a near vision viewing zone in a
lower portion for viewing mainly nearby objects, and an
intermediate vision viewing zone for viewing mainly intermediate
objects between said far and near viewing zones, said far vision
viewing zone and said near vision viewing zone each having an
optical center and a clear vision viewing zone, a predetermined
additional power being added between the optical center of the far
vision viewing zone and the optical center of the near vision
viewing zone along said central basic curve, the gradient G of the
focal power variation between said optical center of the far vision
viewing zone and said optical center of the near vision viewing
zone satisfying the condition:
wherein ADD is said additional power in units of diopter,
the far vision viewing zone in the portion above said optical
center of said far vision viewing zone having said clear vision
viewing zone including said central basic curve and defined by the
condition:
where n is the refractive index of the lens material, and C1 and C2
are the principal curvatures at each point on the refractive
surface of the lens, and wherein m.sup.-1 =1/meter,
the maximum width W (mm) of the said clear vision viewing zone in
said far vision viewing zone satisfying the condition:
8. The spectacles as claimed in claim 7, wherein said gradient G of
the focal power variation of the lens satisfies the condition:
9. The spectacles as claimed in claim 7, wherein the principal
curvatures C1 and C2 of the lens on the central basic curve in said
far vision viewing zone satisfies the condition:
and the direction of the maximum curvature of said principal
curvatures is generally parallel to the horizontal direction.
10. The spectacles as claimed in claim 8, wherein the principal
curvatures C1 and C2 of the lens on the central basic curve in said
far vision viewing zone satisfies the condition:
and the direction of the maximum curvature of said principal
curvatures is generally parallel to the horizontal direction.
11. The spectacles as claimed in claim 7, wherein said intermediate
vision viewing zone includes a clear vision viewing zone, and
wherein the maximum width of the clear vision viewing zone in said
far vision viewing zone of the lens and the maximum width of the
clear vision viewing zone in said near vision viewing zone does not
exceed by four times the minimum width of the clear vision viewing
zone in said intermediate vision viewing zone.
12. The spectacles as claimed in claim 8, wherein said intermediate
vision viewing zone includes a clear vision viewing zone, and
wherein the maximum width of the clear vision viewing zone in said
far vision viewing zone of the lens and the maximum width of the
clear vision viewing zone in said near vision viewing zone does not
exceed by four times the minimum width of the clear vision viewing
zone in said intermediate vision viewing zone.
13. The spectacles as claimed in claim 7, wherein said lenses are
formed so that the eye point is on said central basic curve and at
a portion 5 mm to 15 mm apart from said optical center of the far
vision viewing zone toward said optical center of the near vision
viewing zone.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to progressive multifocal
ophthalmic lenses and, in particular, to a new construction for the
refractive surface of a progressive multifocal lens for use
preferably by an older person. As a person grows older, the
amplitude of accommodation of the eyes becomes weakened. The
present invention provides lenses which compensate for the weakened
eye condition, such as presbyopia, and also provides spectacles
utilizing such progressive multifocal lenses.
Conventional progressive multifocal opthalmic lenses are disclosed
in Maitenaz U.S. Pat. No. 3,910,691 issued on Oct. 7, 1975 and in
Winthrop U.S. Pat. No. 4,062,629 issued on Dec. 13, 1977. A
progressive multifocal ophthalmic lens generally includes a portion
for viewing distant objects at the upper position of the lens and a
portion for viewing nearby objects at the lower position of the
lens. An intermediate section is presented between the upper and
lower portions. The three portions are known generally as the far
vision viewing zone, the near vision viewing zone and the
intermediate vision viewing zone. The zones are generally divided
into left and right parts by a principal meridian curve which
generally extends vertically. In at least the intermediate zone,
the surface power varies progressively. The demarcations of each
vision viewing zone are made to be smooth so that changes from one
zone to the other by the eye are not perceived by the wearer of the
lens.
It is desired to provide an improved progressive multifocal lens
and spectacles using same which achieve each of the objects,
benefits and advantages detailed below.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the present invention, a
progressive multifocal ophthalmic lens is provided. The lens
includes first and second refraction surfaces with the first
refractive surface having a central basic curve defined thereon
which extends essentially vertically therealong and divides the
first refractive surface into a left portion and a right portion.
The lens further includes a far vision viewing zone in an upper
portion thereof for viewing mainly distant objects, a near vision
viewing zone in a lower portion thereof for viewing mainly nearby
objects, and an intermediate vision viewing zone for viewing mainly
intermediate objects between the far and near vision viewing zones.
The far vision viewing zone and the near vision viewing zone each
have an optical center. A predetermined additional power is added
between the optical center of the far vision viewing zone and the
optical center of the near vision viewing zone along the central
basic curve. The gradient G of the focal power variation between
the optical center of the far vision viewing zone and the optical
center of the near vision viewing zone satisfies the condition:
where ADD is the additional power in units of diopters.
The far vision viewing zone in the portion above the optical center
thereof includes a clear vision viewing zone which includes the
central basic curve which is defined by the condition:
where n is the refractive index of the lens material, and C1 and C2
are the principal curvatures at each point on the refractive
surface of the lens, and wherein the measurements are expressed in
units of m.sup.-1 =1/meter.
The maximum width W (mm) of the clear vision viewing zone satisfies
the condition:
The present invention provides an improved progressive multifocal
lens in which a gradient of the additional power variation along
the central basic curve of the progressive multifocal lens is
enough to be easy, the astigmatism on the central basic curve is
minimized, the clear vision viewing zone (the zone in which the
astigmatism is 0.5 diopter or less) in the far vision viewing zone
is much smaller than that of the lens in the prior art, thereby
having a wide and comfortable visual zone in the intermediate
vision viewing zone thereof and reducing the shaking of images
therethrough. The present invention also provides improved
spectacles using the lenses according to the present invention in
which the lenses are set in a frame so that the eye point is on the
central basic curve and at a point 5 mm to 15 mm apart from the
optical center of the far zone toward the optical center of the
near zone and which are suitable for tasks viewing the intermediate
distanced objects or near objects.
Accordingly, it is an object of the present invention to provide
improved progressive multifocal ophthalmic lenses.
Another object of the present invention is to provide a progressive
multifocal ophthalmic lens for use by older people wherein the
amplitude of accommodation of the eyes has become weakened.
A still further object of the present invention is to provide
improved progressive multifocal ophthalmic lenses and spectacles
using same.
Yet another object of the present invention is to provide an
improved progressive multifocal ophthalmic lens in which various
defects are eliminated and which is suitable for tasks wherein
intermediate and near vision viewing is more important.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts which will be
exemplified in the constructions hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to
the folowing description taken in connection with the accompanying
drawings, in which:
FIG. 1A depicts the distribution of astigmatism in a progressive
multifocal ophthalmic lens constructed in accordance with a first
embodiment of the present invention;
FIG. 1B is a graph depicting the focal power variation along the
central basic curve of a lens constructed in accordance with a
first embodiment of the present invention;
FIG. 1C is a front plan view of a portion of a pair of spectacles
which incorporate the progressive multifocal lens constructed in
accordance with a first embodiment of the present invention;
FIG. 2 is a schematic front plan view of a progressive multifocal
lens constructed in accordance with the prior art for use in
explaining the zones thereof;
FIG. 3 is a graph showing the focal power variation along the
central basic curve of a conventional progressive multifocal
ophthalmic lens;
FIGS. 4 and 5 are schematic plan views of progressive multifocal
lens in the prior art showing the distribution of astigmatism
therein;
FIG. 6A is a front plan view of a pair of spectacles which
incorporate progressive multifocal opthalmic lenses from the prior
art wherein the spectacles are designed symmetrically with respect
to the central basic curve;
FIG. 6B is a front plan view of a pair of spectacles which
incorporate progressive multifocal ophthalmic lenses from the prior
art wherein the spectacles are not designed symmetrically with
respect to the central basic curve;
FIG. 7 is a schematic plan view illustrating the distribution of
astigmatism of a progressive multifocal ophthalmic lens constructed
in accordance with a second embodiment of the present
invention;
FIG. 8 is a schematic plan view depicting the distribution of
astigmatism of a progressive multifocal ophthalmic lens constructed
in accordance with a third embodiment of the present invention;
FIG. 9A is a schematic plan view depicting the distribution of
astigmatism of a progressive multifocal ophthalmic lens constructed
in accordance with a fourth embodiment of the present
invention;
FIG. 9B is a front plan view of a portion of a pair of spectacles
using the lens depicted in FIG. 9A;
FIG. 10 is a schematic plan view illustrating the distribution of
astigmatism of a progressive multifocal ophthalmic lens constructed
in accordance with the prior art; and
FIG. 11 is a schematic plan view depicting the distribution of
astigmatism in another progressive multifocal ophthalmic lens
constructed in accordance with the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Progressive multifocal ophthalmic lenses were developed in order to
compensate for the weakened function to control the crystalline
lens of eyes of the aged. The fundamental structure of such lenses
is first described.
Progressive multifocal lenses are formed of a pair of refractive
surfaces including a convex surface and a concave surface. The
convex surface has a surface power which is different partially and
which provides the focal power of lenses which is suitable for
viewing from far objects to near objects. The concave surface
corrects nearsightedness, farsightedness, astigmatism and the like
according to the prescription for each wearer's eyes. It is
possible to form lenses in which the function of the convex surface
and that of the concave surface are exchanged. However, the lenses
of the structure as described above are generally produced because
of the ease of manufacture and the like.
Additionally, the convex lens surface is roughly divided into zones
as shown in FIG. 2 of the drawings provided to help in
understanding the structure of such lenses.
In FIG. 2, the lens is shown as including a far vision viewing zone
or far zone 1, an intermediate vision viewing zone or intermediate
zone 2, and a near vision viewing zone or near zone 3, each having
respective focal powers suitable for viewing far objects (about 1
m, 2 m or more away), intermediate objects (between 50 cm and 1 m
or 2 m away) and near objects (less than 50 cm away), respectively.
The lens includes a central basic curve M, which extends from top
to bottom in the general center of the lens and divides the lens
into right and left portions. If the central basic curve divides
the lens into these two portions symmetrically, it is sometimes
called "the principal meridian curve", and if not, it is sometimes
called "the principal grazing line". The central basic curve plays
very important roles in the structure of the refractive surface of
progressive multifocal lenses. The focal power (or more accurately
the surface power) varies along the central basic curve as shown in
FIG. 3, thus providing the fundamental function of the progressive
multifocal lens.
In FIG. 3, the ordinate shows the point along the central basic
curve and the abscissa shows the focal power. As is clear from the
graph of FIG. 3, the focal power increases gradually from the point
A to the point B (FIG. 2), while it is substantially constant or
changes very little in the regions above point A and below point B.
The turning points A and B of the focal power variation are called
the optical centers of the far zone and the near zone,
respectively.
As shown in FIG. 2, the portion above point A is called the far
zone, the portion below point B is called the near zone, and the
portion between A and B is called the intermediate zone. Since the
focal power varies continuously on the refractive surface of the
progressive multifocal lens, it is impossible to clearly divide the
lens surface into three portions as mentioned above. However, the
conception of dividing the lens surface into three zones is
generally used to facilitate understanding the structure of the
lens.
The increment of the focal power added between the optical center
of the far zone and the optical center of the near zone is called
the additional power. The additional power is generally selected
from a value between 0.5 diopter (hereinafter referred to as "D")
for the slight or mild presbyopia and 3.5 D for the severe
presbyopia.
The focal power on the surface of the lens, that is, the surface
focal power S has the following relation with the curvature C (in
units m.sup.-1 =1/meter) of the surface of lens:
wherein n is a refractive index of lens materials. As a refractive
index of lens material is constant, the curvature is proportionate
to the surface focal power. Accordingly, FIG. 3 may well be
regarded to show the curvature variation along the central basic
curve. As the curvature varies along the central basic curve
extending generally on the center line of the lens, the
configuration of the convex surface of the progressive multifocal
lens is aspherical in the region from the far zone to the near
zone. Hence, the curvature at a point on the lens surface varies
with the direction thereof. Then, the difference of the surface
power as shown by the following formula is represented at a point
of the surface of the lens in proportion to the difference between
the maximum curvature C1 and the minimum curvature C2 (referred to
as the principal curvatures):
This difference of the curvature appears as the astigmatism in
terms of the optical properties of a lens. In the present
description, the astigmatism means the difference of the surface
focal power. FIG. 4 shows the distribution of the astigmatism on
the progressive multifocal lens of the prior art. In FIG. 4, the
astigmatism is shown by lines of the same astigmatism strength just
like contour lines on a map and the narrower a space between
hatched lines is, the larger the astigmatism is. The minimum
astigmatism contour line shows 0.5 D and the white region shows
that the astigmatism is less than 0.5 D. The region with the
astigmatism of less than 0.5 D is referred to as the clear zone
through which a wearer can see objects without perceiving the
blurring of images. Herein, the clear zone is defined correctly as
follows:
wherein C1 and C2 stand for the principal curvatures in units of
m.sup.-1 at each point on the refractive surface in the clear zone
and n is the refractive index of lens materials.
In FIG. 4, M, A and B correspond to those of FIG. 2 and show the
central basic curve, the optical center of the far zone, and the
optical center of the near zone, respectively. The progressive
multifocal lens presents large astigmatism in the lateral portion,
especially in the lateral portion in the intermediate zone and the
near zone of the lens as shown in FIG. 4. This astigmatism is
perceived as the blurring of images when looking at some object
therethrough and also the images are distorted, thereby causing the
shaking of the images when the wearer moves his head. Thus, the
wearer feels uncomfortable because of the astigmatism. Therefore,
it is desired to remove the astigmatism, but it is impossible to
completely do so in view of the fundamental structure of the
progressive multifocal lens. That is, when the astigmatism is
removed by forming the far zone and the near zone to be fully
spherical, the intermediate zone lying smoothly between the far
zone and the near zone is obliged to be transformed remarkably,
thereby causing large astigmatism in the intermediate zone. When
the astigmatism is scattered over the lateral portion by making the
clear zone in the far zone and near zone to be narrow, the
astigmatism in the intermediate zone is reduced and the field of
vision is expanded and the shaking of images is reduced in the
intermediate zone, but the viewing quality through the far zone and
the near zone is deteriorated. Since all progressive multifocal
lenses necessarily have this inherent defect, i.e., astigmatism, it
is necessary to design lenses so as to reduce defects caused by the
astigmatism as much as possible according to the use of an
individual wearer. From this point of view, the progressive
multifocal lenses which have developed so far are roughly
classified into two types as shown in FIGS. 4 and 5.
FIG. 4 shows the distribution of the astigmatism of the progressive
multifocal lens of the prior art in which the far vision viewing
and the near vision viewing are equally considered to be important.
The length between A and B in which the additional power is added
along the central basic curve is normally 12 to 16 mm (a section
between A and B is referred to as the progressive zone and the
length thereof is referred to as the length of the progressive
zone). This length of the progressive zone is not desired to be
very long in view of the facility of rotation of the eyeball from
the far vision viewing of the near vision viewing. The width of the
clear zone in the far zone is at least about 40 mm in the
horizontal direction, so that objects are seen clearly even when
turning eyes into the lateral direction. The width of the clear
zone in the near zone varies depends on the additional power and,
for example, for the lens with the additional power of 2.00 D, the
width of the clear zone is about 10 mm to 15 mm. The width of the
clear zone in the intermediate zone is determined mainly by the
gradient of the focal power variation in the progressive zone and
is normally 3 mm to 5 mm for the lens with the additional power of
2.00 D.
Reference is now made to FIG. 5 which shows the distribution of the
astigmatism of the progressive multifocal lens disclosed in U.S.
Pat. No. 4,537,479 in which the present inventor was involved. The
structure of the lens of FIG. 5 is different from that of the lens
as shown in FIG. 4 since the lens of FIG. 5 is designed considering
the far vision viewing and the intermediate vision viewing to be
more important. That is, in the lens of FIG. 5, by providing the
long progressive zone of 18 mm or more reducing the gradient of the
focal power variation, the clear zone in the intermediate zone is
made wide, and the clear zone in the far zone is made wide over the
lateral peripheral portion of the lens. The width in the horizontal
direction of the clear zone in the near zone is a little wider than
that in the intermediate zone.
Thus, these two types of lenses, namely, the standard type lens in
which both of the far vision viewing and the near vision viewing
are considered more important and the zones in the whole lens are
well balanced as shown in FIG. 4 (hereinafter referred to as the
standard type) and the lens in which the far zone and the
intermediate zone are considered more important as shown in FIG. 5
(hereinafter referred to as the far and intermediate type), are
those utilized according to the use in the prior art.
Spectacles or eyeglasses using such progressive multifocal lenses
are now described.
In manufacturing spectacles, a circular lens as shown in FIG. 4 is
cut into the configuration of the frames of the spectacles and put
into frames. At this time, the lens must be set so that the eye
point is on the proper position. The eye point is a point of the
lens through which the line of vision passes when the wearer looks
at the far vision in a natural posture and it is also referred to
as a fitting point. The eye point should be defined especially
correctly in the progressive multifocal lens. As mentioned above,
in the progressive lens, the power varies from point to point on
the surface thereof and the distribution of the astigmatism is
peculiar, and so the inherent properties of the progressive
multifocal lens do not function without setting the eye point
correctly.
FIGS. 6A and 6B are front plan views showing the structure of
spectacles using the progressive multifocal lenses of the prior
art, in which the region surrounded by a dotted line is the clear
zone. In the spectacles of the type of FIGS. 6A and 6B, the eye
point E is set either on the same point as the optical center of
the far zone A (as shown in FIG. 6A) or at the point about 2 to 4
mm above the optical center of the far zone (as shown in FIG. 6B)
of the lens. Herein, FIG. 6A illustrates an example of the
spectacles in which the clear zone of the lens is symmetrical with
respect to the central basic curve and the lenses are framed so as
to have the central basic curve inclined by about 10.degree. so
that the optical center of the near zone is closer to the nose side
than the optical center of the far zone according to the
convergence of the eyeballs as shown in the drawing. FIG. 6B
illustrates another example of the spectacles in which the central
basic curve is previously bent in consideration of convergence of
the eyeballs and in such a case, it is not necessary to incline the
lenses at the time of framing. Herein, there is no relation between
the symmetrization on design and the position of the eye point.
The reason for defining the eye point at the center of the far zone
or the point slightly above that is that, in daily life, it is
normally required for the wearer to be able to view far objects
when he looks forward in a natural posture. In order to meet this
requirement, the eye point is defined at the position which is in
the far zone and where the rotation of eyes is not too large when
viewing the near vision, i.e., near the optical center of the far
zone. This feature is also applied to the far and intermediate type
progressive multifocal lens.
As mentioned above, the progressive multifocal lens should be
designed so as to optimally achieve the purpose of a user by
eliminating problems as much as possible. In this sense, the
conventional progressive multifocal lenses are less than
satisfactory in use in the tasks in which the intermediate vision
viewing and the near vision viewing are mainly performed, such as
writing, medical operations like surgery, machine working with
tools such as a lathe and the like. The standard type lens is
indeed convenient to use because the far zone and the near zone
have wide clear zones and rotation of the eyes when the line of
vision moves from the far vision to the near vision is small, but
when the intermediate zone is narrow and especially where the
additional power is over 2.5 D, the wearer feels as if he peers out
through the small open space of a door and feels discomfort at the
time of intermediate vision viewing. The far and the intermediate
type lens, which has a very wide clear zone in the intermediate
zone, wider than that of the standard type lens, provides a good
vision in the far vision viewing and the intermediate vision
viewing. However, in this type of lens, the near zone is far from
the eye point and narrow and so the near vision viewing is
inconvenient.
The present invention provides a progressive multifocal lens and
spectacles using the same in which the defects as above are
eliminated and which is suitable for tasks with viewing mainly the
intermediate and near visions. The present inventor has studied the
various factors which determine the performance of the progressive
multifocal lens with respect to the progressive multifocal lens in
the prior art and newly manufactured experimental lenses and the
following results have been obtained.
First, in order to obtain a lens which has the wide clear zone in
the intermediate zone thereof and which is convenient to use, the
gradient G of the additional power along the central basic curve in
the intermediate zone is defined by the formula:
wherein ADD is the additional power of the lens. The smaller the
gradient G in the intermediate zone is, the better, regardless of
the additional power. However, as the desired additional power
needs to be realized in the limited space of spectacles, the
balance of the gradient G of the focal power along the central
basic curve and the desired additional power is considered and as a
result the above formula is obtained.
Further, in the case where the wide intermediate vision viewing is
needed, such as in a surgical operation, and the additional power
for the spectacles of a wearer's prescription is more than 2.5 D,
the gradient G is desired to satisfy the condition:
Furthermore, in order to surely obtain the minimum visual field
necessary for the far vision viewing and to reduce the astigmatism
in the lateral portions of the intermediate zone, the maximum width
W in the horizontal direction of the clear zone in the far vision
should satisfy the condition:
Herein, the astigmatism is scattered into the far zone, and
consequently, the astigmatism in the lateral portions of the
intermediate zone is greatly reduced.
The value of W is defined within the range as depending upon the
degree of the requirement for the far vision viewing and the degree
of the astigmatism allowed in the lateral portions of the
intermediate zone. The wearing tests for the present invention have
shown that with respect to the lens in which a portion available
for the far vision viewing is less than about 5 mm, the wearer
complains about the width of the far vision, and with respect to
the lens in which a portion available for the far vision viewing is
more than about 30 mm, the wearer complains about the blurring and
shaking of images in the visual field through the lateral portions
of the intermediate zone.
Especially, when the wide visual field from far to near is
required, it is effective to provide the astigmatism of 0.2 to 0.3
D which has the maximum focal power into the horizontal direction
along the central basic curve in the far zone. Namely, by
scattering the astigmatism in the far zone even over the central
basic curve, the astigmatism in the intermediate zone is
significantly reduced. Moreover, such a degree of the astigmatism
as 0.2 to 0.3 D hardly makes a wearer feel the blurring of images
when viewing distant objects.
Also, when the shaking of images through the intermediate zone is
to be reduced, it has been proved to be necessary to provide
certain conditions between each clear viewing zone in the far zone,
the intermediate zone, and the near zone. Namely, it is effective
to design so that the maximum width in the horizontal direction of
the clear zone in the far zone and that in the near zone do not
exceed four times the minimum width of clear zone in the
intermediate zone. By satisfying this condition, the distribution
of the astigmatism in the lateral portions from the far zone to the
intermediate zone and to the near zone becomes smooth and changes
easily, and the shaking of images is reduced. The above mentioned
ratio of the width of the clear viewing zones is allowed to be
large as regards the lens of the small additional power through
which the shaking of images is primarily small. However, as regards
the lens of the large additional power more than 2.5 D, the ratio
is preferably less than three times.
Thereafter, utilizing these progressive multifocal lenses, the
spectacles were made so that the eye point was at the point 5 to 15
mm lower than the optical center of the far zone along the central
basic curve. By designing the spectacles as above, the power of
lenses is suitable to the wearer's eyes when he views the
intermediate objects in front of his face and accordingly the
spectacles are convenient to see the intermediate vision.
In the progressive multifocal lens according to the present
invention, the gradient of the focal power variation on the central
basic curve is made small and so the distance between the optical
centers of the far zone and of the near zone is long. In such a
case, if the eye point is at the position as in the prior art, the
near zone must be in an extremely low portion of the lens, thereby
making it considerably difficult to view the near vision. However,
the lens with the eye point located as mentioned above in the
present invention allows the wearer to view the near vision only if
he puts the line of vision downward as he does with the progressive
multifocal lenses in the prior art.
Herein, the location of the eye point is determined according to
the necessity of the far vision viewing; the more the necessity
thereof is, the nearer to the optical center of the far zone the
eye point should be.
The progressive multifocal lens according to the present invention
is described in detail with reference to several embodiments.
FIGS. 1A and 1B depict the distribution of astigmatism and the
variation of the focal power along the central basic curve,
respectively, of the first embodiment of the progressive multifocal
lens according to the present invention.
In FIG. 1A, M is the central basic curve, A is the optical center
of the far zone, and B is the optical center of the near zone. The
numerals in FIG. 1A show the astigmatism of each contour line in
units of diopter. This embodiment is directed to the lens with the
additional power of 2.0 D, in which the optical center A of the far
zone and the optical center B of the near zone are at the points 10
mm above and 15 mm below, respectively, the geometric center 0 of
the lens.
The focal power in the progressive portion varies approximately
linearly along the central basic curve M as shown in FIG. 1B and
the gradient G of the focal power variation is expressed by the
formula:
In the embodiments of the present invention disclosed hereinafter,
the focal power variation is approximately linear, so the
description thereof is omitted. The astigmatism on the central
curve is zero. That is, the central basic curve is the umbilical
curve. The maximum width W in the horizontal direction in the far
zone is about 18 mm.
FIG. 10 shows the distribution of the prior art progressive
multifocal lens for comparison with the lens of FIG. 1A according
to the present invention. The lens of FIG. 10 has the additional
power of 2.0 D and the progressive zones as long as 16 mm in which
the focal power variation is almost linear. Accordingly, the
gradient G of the focal power variation in the progressive zone
satisfies the equation G=2.0/16=0.125 (D/mm). The astigmatism on
the central basic curve is zero and the maximum width W in the
horizontal direction of the far zone is 42 mm. The maximum width in
the horizontal direction of the clear zone in the near zone is
about 12 mm in both lenses of FIG. 1A and FIG. 10.
The progressive multifocal lens according to the present invention
is characterized in that the gradient of the focal power variation
along the central basic curve in the progressive portion is far
smaller and the maximum width in the horizontal direction of the
clear zone in the far zone is even smaller compared with the prior
art lens mentioned above. The effect of the characteristic is
reflected on the intermediate zone. Namely, as is clear by
comparing FIG. 1A with FIG. 10, the astigmatism in the intermediate
zone is significantly smaller in the lens according to the present
invention than that in the prior art lens. Comparing the width in
the horizontal direction of the clear zone of the intermediate zone
between the lenses in FIG. 1A and FIG. 10, that of the lens
according to the present invention is about 7 mm and is
approximately 40% larger than that in the prior art lens. Also,
with respect to the astigmatism in the lateral portions from the
intermediate zone to the near zone of the lens, that of the prior
art lens is 2.5 D while that of the lens according to the present
invention is only 1.5 D. Accordingly, the present invention
provides the lens through which the wearer obtains a wide field of
vision without feeling like peeping out of a small space of a door.
Moreover, when the wearer moves the line of vision from the
intermediate zone to the near zone of the lens, the field of vision
is smooth and natural.
The ratio of the widths of the clear zones in the far zone and the
near zone with respect to the width of the clear zone in the
intermediate zone is about 2.3 times and 1.5 times, respectively,
which are extremely reduced compared with about 8.4 times and 5.4
times, respectively, of the prior art lens. This is another
characteristic of the present invention. Thus, by smoothing the
abrupt decrease of the width of the clear zone in the intermediate
zone, the astigmatism is prevented from concentrating in the
lateral portions of the intermediate zone as in the prior art
lenses, and consequently the shaking of images is reduced.
FIG. 7 depicts the distribution of the astigmatism of the second
embodiment of the progressive multifocal lens according to the
present invention. In this embodiment, the additional power is 2.0
D as in the first embodiment, the optical center A of the far zone
and the center B of the near zone are on the central basic curve 15
mm above and 15 mm below, respectively, the geometric center 0.
The maximum width W in the horizontal direction of the clear zone
in the far zone is about 10 mm. There is the astigmatism partially
on the central basic curve, which is different from the first
embodiment. Namely, in the far zone, there is the astigmatism of
2.5 D which has the maximum focal power in the horizontal
direction, and in the intermediate zone, the astigmatism decreases
almost linearly form the optical center of the far zone toward the
optical center of the near zone until it becomes zero at the
optical center of the near zone. The maximum width of the clear
zone in the near zone is about 14 mm.
In this embodiment, the gradient G of the focal power variation in
the progressive zone is shown as G=2.0/30=0.067 (D/mm) which is
even smaller than that of Embodiment 1. Consequently the width in
the horizontal direction of the clear zone in the intermediate zone
becomes wide, thereby improving the intermediate vision viewing in
terms of not only the dimension of a visual field but also the
shaking of images. Furthermore, since the astigmatism is provided
along the central basic curve in the far zone in this embodiment,
the astigmatism as above necessarily occurs in the progressive
zone, too, and the clear zone in the intermediate zone laterally
expands as it becomes closer to the near zone. Accordingly, the
lens of this embodiment is more convenient in that the transition
of the intermediate vision viewing and the near vision viewing is
smooth and comfortable.
The lenses of the second embodiment are especially designed for the
use in tasks using the intermediate and near vision viewing. So,
the width of the far zone is more greatly narrowed than that of
Embodiment 1 so as to improve the intermediate vision viewing. The
width of the clear zone in the intermediate zone is the narrowest
near the optical center of the far zone and is about 5 mm, and the
widest at the region 5 to 8 mm below the geometric center and is
about 20 mm. Similar to the first embodiment, the ratio of the
maximum width of the clear zone of the far zone and the near zone
with respect to the minimum width of the clear zone of the
intermediate zone is 2 times and 2.4 times, respectively and thus
the decrement of the width of the clear zone in the intermediate
zone is less than two-thirds of those of the far and the near
zones.
FIG. 8 illustrates the distribution of the astigmatism of the third
embodiment of the progressive multifocal lens according to the
present invention. In this Embodiment, the additional power is 2.5
D and the optical centers of the far zone and the near zone are
positioned in the same locations as those of Embodiment 1. The
astigmatism on the central basic curve is zero. The width W of the
clear zone in the horizontal direction is the far zone is about 13
mm and the width in the near zone is about 12 mm.
FIG. 11 shows the distribution of the astigmatism of the prior art
progressive multifocal lens for comparison with this embodiment. In
FIG. 11, the additional power is 2.5 D, the length of the
progressive zone is 16 mm, the width W of the clear zone of the far
zone is 40 mm, that of the near zone is about 12 mm and the
astigmatism on the central basic curve is zero.
By comparing FIG. 8 with FIG. 11, the effects of the present
invention as described with respect to the lens with the additional
power of 2.0 D can be reconfirmed. That is, in the prior art, the
width of the clear zone in the intermediate zone is about 3.5 mm,
while that of the lens of the present invention is about 5 mm and
is 40% larger than in the prior art. The astigmatism of the lateral
portions extending in the intermediate zone and in the near zone is
3.0 D in the prior art, while it is 1.5 D in the present invention,
being greatly reduced, so that the dimension of the visual field
and the shaking of the images for the intermediate zone are
remarkably improved.
The ratio of the clear zone of the far zone with respect to that of
the intermediate zone is about 11 times in the prior art, while
about 2.6 times in the present invention. The ratio of the clear
zone of the near zone with respect to that of the intermediate zone
is about 3.4 times in the prior art, while 2.4 times in the present
invention being reduced remarkably and the shaking of images
through the intermediate zone is reduced.
FIG. 9A shows the distribution of the astigmatism of the fourth
embodiment of the progressive multifocal lens according to the
present invention. The additional power of the lens is 2.5 D as in
Embodiment 3 and the centers of the far zone and the near zone are
positioned 15 mm above and 15 mm below the geometric center 0 of
the lens respectively. The maximum width W of the clear zone in the
far zone is about 8 mm and the width of the clear zone in the near
zone is about 10 mm. The lens of FIG. 9A has the astigmatism on the
central basic curve as in Embodiment 2 shown in FIG. 7. As is clear
from comparison of FIG. 9A with FIG. 8, similar to the second and
the first embodiments, as a result of the gradient of the focal
power variation in the progressive zone being reduced, since the
astigmatism is provided on the central basic curve in the far zone
and since the width of the clear zone of the far zone is narrowed,
the astigmatism in the intermediate zone is drastically reduced and
the intermediate vision viewing is improved.
With reference to the configuration of the clear zone in the
intermediate zone, the minimum width thereof near the optical
center of the far zone is about 4 mm and the maximum width thereof
a little below the geometric center is about 8 mm. Accordingly, the
maximum width of the clear zone of the far zone and the near zone
is about twice and 2.5 times as large as the minimum width of the
clear zone of the intermediate zone, respectively, to control the
shaking of images.
Next, spectacles according to the present invention are explained
in detail with reference to several of the embodiments.
FIGS. 1C and 9B show embodiments of spectacles according to the
present invention. Both of these drawings are front plan views of
one half of the spectacles using the progressive multifocal lenses
of Embodiments 1 and 4, respectively, in which the progressive
multifocal lens according to the present invention is put into
frames F of spectacles. In the drawings, the region inside of the
dotted lines is the clear zone of the lens. The eye point E, in
FIG. 1C is 10 mm below the optical center A of the far zone and in
FIG. 9B it is 15 mm below the optical center A of the far zone on
the central basic curve. The characteristic of the spectacles
according to the present invention is that the progressive
multifocal lenses according to the present invention as described
above are used and are put into frames so that the eye point is
within the progressive zone, concretely at the position 5 to 15 mm
below the optical center of the far zone. By the structure as
above, the following features in the practical use are obtained.
When the wearer of the spectacles can look forward, the focus of
the lens is at the intermediate distant point from the wearer's
eyes and so the wearer can view the intermediate zone comfortably
by looking straight forward. When the wearer looks from straight
forward to downward through lenses, he can see the near vision
through the near zone as in the progressive multifocal lenses in
the prior art. While, as the wearer looks upwards from straight
forward, the focus of the lens moves far away, so it is capable to
look at the far vision viewing through the portion above the
optical center of the far zone.
Such spectacles as above are different from any others known in the
prior art. The reasons are that the spectacles using the
progressive multifocal lenses in the prior art are designed
considering the far vision viewing to be most important and so it
is necessary to set the eye point within the far zone as shown in
FIGS. 6A and 6B and that the lenses in themselves in the prior art
have defects of narrow visual field through the intermediate zone
and of the considerable shaking of images and so the spectacles as
in the present invention cannot be realized from the prior art.
Accordingly, the spectacles according to the present invention are
advantageous in the tasks with viewing the intermediate and the
near visions and have a feature that the wearer can look not only
at near objects but also use the far vision, though it is not very
wide unlike the single vision lenses for the aged people in the
prior art.
As explained with reference to the embodiments, the present
invention provides improved progressive multifocal lenses and
spectacles using the same which are suitable for the tasks mainly
with the intermediate and the near vision viewing.
The progressive multifocal lens in accordance with the present
invention is designed so as to define the gradient G of the
additional power variation in the intermediate zone to satisfy the
condition:
wherein ADD is the additional power, so that the clear zone in the
intermediate zone is expanded and consequently a wide and clear
image is obtained for the intermediate vision viewing.
Simultaneously, by providing the astigmatism in the far zone so
that the maximum width W in the horizontal direction of the clear
zone in the far zone satisfies the condition W.ltoreq.30 (mm), the
astigmatism in the intermediate zone is further reduced and the
blurring and shaking of images through the lateral portions of the
intermediate zone of the lens are reduced. Additionally, the width
W of the clear zone in the far zone as above is defined as
W.gtoreq.5 (mm) to insure the quality of the vision viewing which
is necessary at the minimum.
When the gradient G of the focal power variation along the central
basic curve in the intermediate zone is defined so as to satisfy
the condition: G.ltoreq.ADD/25 (D/mm), the astigmatism in the
intermediate zone is far more reduced and a very good intermediate
vision viewing is obtained.
By adding the astigmatism of 0.2 to 0.3 D which has the maximum
focal power nearly in the horizontal direction onto the central
basic curve in the far zone, the clear zone in the intermediate
zone presents the configuration which expands from the far zone
side to the near zone side, and consequently it becomes especially
easy to see the intermediate and near objects through the
lenses.
By defining the maximum width in the horizontal direction of the
clear zone in the far zone and the near zone not be be larger than
4 times of the minimum width of the clear zone in the intermediate
zone, the astigmatism in the lateral portions of the lens gradually
varies over the region from the far zone to the near zone and the
shaking of images for the intermediate vision viewing is reduced
because the astigmatism is not concentrated to the lateral portion
of the intermediate zone as it is in the lenses in the prior art.
The ratio of the maximum width of the clear zone of the far and the
near zones with respect to the minimum width of that of the
intermediate zone is preferably less than 3 times with respect to
the lens whose additional power is more than 2.5 D.
The spectacles in accordance with the present invention are made of
the lenses having the superior performances for the intermediate
vision viewing as mentioned above and the lenses are framed so that
the eye point is at the point on the central basic curve 5 mm to 15
mm away from the optical center of the far zone toward the optical
center of the near zone. By this structure, the wearer can
comfortably view intermediate objects when looking straight forward
from the face and the spectacles are very convenient to use in
tasks performed mainly with the intermediate and near vision
viewing.
As mentioned above, the progressive multifocal lens and spectacles
using the same which are suitable for tasks performed mainly with
the intermediate and the near vision viewing are obtained according
to the present invention. The features of the progressive
multifocal lens and those of the spectacles are selected in
combination according to the uses.
Moreover, in the embodiments of the present invention, lenses are
designed symmetrically with respect to the central basic curve.
However, the concept of the present invention is also applicable to
the lenses which are asymmetrical laterally being designed in
consideration of the convergence of the eyeball.
Moreover, the focal power variation in the progressive zone is
nearly linear in all of the embodiments but it is not a necessary
condition for the present invention.
Furthermore, the present invention can be applied to the
progressive multifocal lenses having the progressive focal power
variation on the concave refractive surface of the lens.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
constructions without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
* * * * *